Texture stretching at edge even though UV map says it's fine
The distortion in your unwrap may be caused by:


modifier options: some modifiers (e.g. solidify) can add som distortion to your unwrap
geometry errors: for example duplicated vertices or overlapping faces
uvs are not relaxed enough


So, first of all check your geometry. If your model is perfect, then you have two options:


unwrap again the faces which have the distortion
pin the borders of your shells and update the uv coordinates (a pinned vertex will keep it's position also if you try to unwrap the entire model)


I would suggest to apply the last option, and to do that:


in UV/Image Editor select the border edges of your shells and press P to pin these vertices (now are red colored)

select all the shells (with A for example) and then press E, so you will update the uv coordinates for all vertices except the pinned ones